Deere Magneto to Distributor Question

[dunncl66]

When a magnetor is swap with a distributor and a coil is a ballast resistor required? I have a 50 with a distributor and the coil is getting pretty hot when it runs and I am wondering if I need a resistor like a car.

 

[Jim.ME]

What temperature is "pretty hot".

The answer depends on the system voltage and the coil you purchase. A 6-volt coil on a 6-volt system does not need a ballast resistor. A true 12-volt coil (a coil with the proper size wire and number of internal windings) does not need a ballast resistor. A 6-volt coil used on a 12-volt system needs a ballast resistor, or resistor wire, between it and the switch. This includes coils that have wording on them such as 12-volt external resistor required, those are 6-volt coils in disguise.

I believe the 50 was 12 volts originally and the distributor equipped ones had a resistor in the harness, or on the switch. I don't know if the resistor was in place, but not used, on the engines equipped with magneto ignitions. Did you do the magneto to distributor swap? If the power comes direct from the switch to the coil (a new wire) with no resistor which coil was installed determines whether or not it needs a resistor. You can take an ohm meter reading across the two small terminals of the coil (unhook the wires) to determine if it is 6 or 12 volts. A 6-volt coil should read about 1.5 ohms and a 12-volt coil will read 3 to 4 ohms. Current through the points should be in the 3-to-4-amp range.

 

[dunncl66]

The coil skin temp is painful to touch so I am guessing it’s 150 degrees give or take after 5 mins of run time. I did not perform any work on the tractor yet as I just got it. I will do the ohm meter work - thanks for the advise.

 

[Rich'sToys]

I believe my 50 has a 6 volt coil with a resistor. If I remember correctly, it's set up so it bypasses the resistor when starting the tractor. Been a while since I've worked on it.

I don't believe 50's ever came with a magneto.

 

[HFP]

As Jim said, measure the resistance across the primary coil. That will tell you for sure if you need to run a resistor or not.

 

[Fixingfarmer]

The original resistor will be on the key switch round ceramic encased cylinder. It will be 6v original coil 1.5 ohm across the coil 1.5 ohm across the resistor at the back of the switch

A lot of people change out the key switch to the cheaper one. The original switch will look externally like a master switch I believe with no key. You can also purchase a key switch that has the resistor on the back and the key but it’s a tighter fit under that dash. Both are available with or without a resistor

personally I like the cheap A4699R 2 position switch with removable key paired with a 3 ohm 12 volt coil and skip any resistors but it can be whatever you have laying around. It sounds like you get to make the decision so that’s what I’d pick and yes it’s replacing both items if that isn’t what you have but it’s simple

 

[buickanddeere]

How many Amps through the coil when the points are closed ?

 

[dunncl66]

Coil has 1.2 ohms across it so I am guessing a resistor is needed to get to the 3 ohms

 

[dunncl66]

Got a 3 ohm coil to cut out the resistor, all is good now. I now now all about ignitions coils, thanks all.

 

[55 50 Ron]

The original resistor will be on the key switch round ceramic encased cylinder. It will be 6v original coil 1.5 ohm across the coil 1.5 ohm across the resistor at the back of the switch

A lot of people change out the key switch to the cheaper one. The original switch will look externally like a master switch I believe with no key. You can also purchase a key switch that has the resistor on the back and the key but it’s a tighter fit under that dash. Both are available with or without a resistor

personally I like the cheap A4699R 2 position switch with removable key paired with a 3 ohm 12 volt coil and skip any resistors but it can be whatever you have laying around. It sounds like you get to make the decision so that’s what I’d pick and yes it’s replacing both items if that isn’t what you have but it’s simple

What model tractor are you talking about here? I'm confused by what you said, if you are talking about a John Deere Model 50. There is no A4699R part number in the 50 parts list.